Refactored do_sorting_view to get start_index default value from len(indexes) rather than duplicate the line and set to 0.

Added NonSortableParentAdmin class to enable sorting URLs and JavaScript on models that do not inherit from Sortable.
Removed unused 'ordering' property on SortableAdmin.
Changed assignment of sorting_filters to use getattr, enabling NonSortableParentAdmin to inherit from SortableAdminBase.
Moved template properties to SortableAdminBase.

adminsortable/admin.py

@@ -27,6 +27,14 @@ STATIC_URL = settings.STATIC_URL
 
 
 class SortableAdminBase(object):
+    sortable_change_list_with_sort_link_template = \
+        'adminsortable/change_list_with_sort_link.html'
+    sortable_change_form_template = 'adminsortable/change_form.html'
+    sortable_change_list_template = 'adminsortable/change_list.html'
+
+    change_form_template_extends = 'admin/change_form.html'
+    change_list_template_extends = 'admin/change_list.html'
+
     def changelist_view(self, request, extra_context=None):
         """
         If the model that inherits Sortable has more than one object,
@@ -45,7 +53,7 @@ class SortableAdminBase(object):
         extra_context.update({
             'change_list_template_extends': self.change_list_template_extends,
             'sorting_filters': [sort_filter[0] for sort_filter
-                in self.model.sorting_filters]
+                in getattr(self.model, 'sorting_filters', [])]
         })
         return super(SortableAdminBase, self).changelist_view(request,
             extra_context=extra_context)
@@ -56,15 +64,6 @@ class SortableAdmin(SortableAdminBase, ModelAdmin):
     Admin class to add template overrides and context objects to enable
     drag-and-drop ordering.
     """
-    ordering = ('order', 'id')
-
-    sortable_change_list_with_sort_link_template = \
-        'adminsortable/change_list_with_sort_link.html'
-    sortable_change_form_template = 'adminsortable/change_form.html'
-    sortable_change_list_template = 'adminsortable/change_list.html'
-
-    change_form_template_extends = 'admin/change_form.html'
-    change_list_template_extends = 'admin/change_list.html'
 
     class Meta:
         abstract = True
@@ -89,6 +88,7 @@ class SortableAdmin(SortableAdminBase, ModelAdmin):
         Custom admin view that displays the objects as a list whose sort
         order can be changed via drag-and-drop.
         """
+
         opts = self.model._meta
         has_perm = request.user.has_perm('{0}.{1}'.format(opts.app_label,
             opts.get_change_permission()))
@@ -226,17 +226,17 @@ class SortableAdmin(SortableAdminBase, ModelAdmin):
                     id=model_type_id).model_class()
                 objects_dict = dict([(str(obj.pk), obj) for obj in
                     klass.objects.filter(pk__in=indexes)])
-                if '-order' in klass._meta.ordering:  # desc order
+
+                if '-order' in klass._meta.ordering:
+                    step = -1
                     start_object = max(objects_dict.values(),
                         key=lambda x: getattr(x, 'order'))
-                    start_index = getattr(start_object, 'order') \
+                else:
-                        or len(indexes)
+                    step = 1
-                    step = -1
-                else:  # 'order' is default, asc order
                     start_object = min(objects_dict.values(),
                         key=lambda x: getattr(x, 'order'))
-                    start_index = getattr(start_object, 'order') or 0
+
-                    step = 1
+                start_index = getattr(start_object, 'order', len(indexes))
 
                 for index in indexes:
                     obj = objects_dict.get(index)
@@ -252,6 +252,12 @@ class SortableAdmin(SortableAdminBase, ModelAdmin):
             content_type='application/json')
 
 
+class NonSortableParentAdmin(SortableAdmin):
+    def changelist_view(self, request, extra_context=None):
+        return super(SortableAdminBase, self).changelist_view(request,
+            extra_context=extra_context)
+
+
 class SortableInlineBase(SortableAdminBase, InlineModelAdmin):
     def __init__(self, *args, **kwargs):
         super(SortableInlineBase, self).__init__(*args, **kwargs)